Method and apparatus for laser drilling blind vias

Abstract

In an embodiment, a method of forming a blind via in a substrate comprising a mask layer, a conductive layer, and a dielectric layer is provided. The method includes detecting the mask layer by a sensor, the mask layer providing a substrate surface; determining a property of the blind via, the property comprising one or more of a top diameter, a bottom diameter, a volume, or a taper angle; focusing a Gaussian laser beam, under laser process parameters, at the substrate surface to remove at least a portion of the mask layer; adjusting the laser process parameters based on the property; and focusing the laser beam, under the adjusted laser process parameters, to remove at least a portion of the dielectric layer within the volume to form the blind via. The mask layer can be pre-etched. Apparatus for forming a blind via in a substrate are also provided.

What is claimed is: 
     
       1. A method of forming a blind via in a substrate, comprising:
 conveying the substrate to a scanning chamber of a laser drilling system having a galvanometer scanner, a beam expander, and a collimator coupled to a femtosecond laser source configured to emit a Gaussian laser beam, the substrate comprising:
 a conductive layer, 
 a dielectric layer disposed on at least a portion of the conductive layer, and 
 a mask layer disposed on at least a portion of the dielectric layer; 
 
 detecting a height of the mask layer by a height sensor of the laser drilling system, the mask layer providing a substrate surface; 
 determining one or more properties of the blind via, the one or more properties of the blind via comprising:
 a top diameter of the blind via and a bottom diameter of the blind via, the blind via having a height from the top diameter to the bottom diameter, the top diameter being greater than the bottom diameter; 
 a volume of the blind via, the volume corresponding to the top diameter, the bottom diameter, and the height of the blind via; or 
 a taper angle of about 80 degrees or more; 
 
 removing at least a portion of the mask layer by focusing a Gaussian laser beam emitted from the femtosecond laser source of the laser drilling system, under laser process parameters, at the substrate surface; 
 after removing the at least a portion of the mask layer, adjusting the laser process parameters based on signals from the height sensor regarding the height of the mask layer and the one or more determined properties; 
 removing at least a portion of the dielectric layer within the volume by focusing the Gaussian laser beam using the beam expander, the collimator, and the galvanometer scanner, under the adjusted laser process parameters, to form the blind via; and 
 removing the mask layer from the substrate. 
 
     
     
       2. The method of  claim 1 , wherein the laser process parameters comprise a laser power, a laser energy in a burst, a focal beam diameter, a focus height, a burst energy, a pulse energy, a number of pulses in a burst, a pulse frequency, a burst frequency, a beam spot size, an M 2  value, an offset of beam focusing from substrate surface, or combinations thereof. 
     
     
       3. The method of  claim 1 , wherein the laser process parameters comprise:
 an amount of laser energy in a burst of about 5 μJ or more; 
 a focal beam diameter that is from about 2 μm to about 10 μm for drilling 5 μm diameter vias; 
 a focal beam diameter that is from about 7 μm to about 12 μm for drilling 10 μm diameter vias; 
 a focus height that is from about 0 μm to about 50 μm; 
 a pulse frequency that is about 500 MHz or more; 
 a number of pulses in a burst that is about 2 or more; 
 a number of bursts of about 2 or more; 
 a burst frequency of about 100 kHz or more; or 
 combinations thereof. 
 
     
     
       4. The method of  claim 1 , wherein the top diameter is about 10 μm or less. 
     
     
       5. The method of  claim 1 , wherein:
 the mask layer comprises Al, Cu, W, Mo, Cr, or combinations thereof; and 
 the mask layer has a height of about 2 μm or less. 
 
     
     
       6. The method of  claim 5 , wherein when the mask layer comprises Mo or W, the method further comprises depositing a layer of copper on the mask layer. 
     
     
       7. The method of  claim 1 , wherein the femtosecond laser source is a femtosecond ultraviolet laser with a wavelength of about 400 nm or shorter. 
     
     
       8. The method of  claim 5 , wherein the mask layer comprises Cr. 
     
     
       9. A method of forming a blind via in a substrate, comprising:
 conveying the substrate to a scanning chamber of a laser drilling system having a galvanometer scanner, a beam expander, and a collimator coupled to a femtosecond laser source configured to emit a Gaussian laser beam, the substrate comprising:
 a conductive layer of about 2 μm or more in height, 
 a dielectric layer disposed on at least a portion of the conductive layer, and 
 a pre-etched mask layer disposed on at least a portion of the dielectric layer, the pre-etched mask layer having blind via openings to expose at least a portion of the dielectric layer, the at least a portion of the dielectric layer providing a substrate surface; 
 
 detecting the blind via openings of the pre-etched mask layer by a height sensor of the laser drilling system, the height sensor configured to determine a height of the pre-etched mask layer; 
 determining one or more properties of the blind via, the one or more properties of the blind via comprising:
 a top diameter of the blind via and a bottom diameter of the blind via, the blind via having a height from the top diameter to the bottom diameter, the top diameter being greater than the bottom diameter, and the top diameter corresponding to the blind via openings; 
 a volume of the blind via, the volume corresponding to the top diameter, the bottom diameter, and the height of the blind via; or 
 a taper angle of 80 degrees or more; 
 
 removing a first portion of the dielectric layer within the volume of the blind via, without causing more than half of the thickness of mask layer damage to the pre-etched mask layer, by focusing a Gaussian laser beam emitted from the femtosecond laser source of the laser drilling system, under laser process parameters, at the substrate surface; 
 after removing the first portion of the dielectric layer, adjusting the laser process parameters based on signals from the height sensor and the one or more properties; 
 removing a second portion of the dielectric layer within the volume by focusing the Gaussian laser beam using the galvanometer scanner, the beam expander, and the collimator, under the adjusted laser process parameters, to form the blind via; and 
 removing the pre-etched mask layer from the substrate. 
 
     
     
       10. The method of  claim 9 , wherein the laser process parameters comprise a laser power, a laser energy in a burst, a focal beam diameter, a focus height, a burst energy, a pulse energy, a number of pulses in a burst, a pulse frequency, a burst frequency, a beam spot size, an M 2  value, an offset of beam focusing from substrate surface, or combinations thereof. 
     
     
       11. The method of  claim 9 , wherein the laser process parameters comprise:
 an amount of laser energy in a burst of about 5 μJ or more; 
 a focal beam diameter that is from about 2 μm to about 10 μm for drilling 5 μm diameter vias; 
 a focal beam diameter that is from about 7 μm to about 12 μm for drilling 10 μm diameter vias; 
 a focus height that is from about 0 μm to about 50 μm; 
 a pulse frequency that is about 500 MHz or more; 
 a number of pulses in a burst that is about 2 or more; 
 a number of bursts of about 2 or more; 
 a burst frequency of about 100 KHz or more; or 
 combinations thereof. 
 
     
     
       12. The method of  claim 9 , wherein the top diameter is about 10 μm or less. 
     
     
       13. The method of  claim 9 , wherein:
 the pre-etched mask layer comprises Al, Cu, W, Mo, Cr, or combinations thereof; and 
 the pre-etched mask layer has a height of 3 μm or less. 
 
     
     
       14. The method of  claim 9 , wherein when the pre-etched mask layer comprises Mo or W, the method further comprises depositing a layer of copper on the pre-etched mask layer. 
     
     
       15. The method of  claim 13 , wherein the mask layer comprises Cr. 
     
     
       16. A method of forming a blind via in a substrate, comprising:
 conveying the substrate to a scanning chamber of a laser drilling system having a galvanometer scanner, a beam expander, and a collimator coupled to a femtosecond laser source configured to emit a Gaussian laser beam, the substrate comprising:
 a conductive layer, 
 a dielectric layer disposed on at least a portion of the conductive layer, and 
 a mask layer disposed on at least a portion of the dielectric layer, the mask layer comprising Al, Cu, W, Mo, Cr, or combinations thereof, and the mask layer having a height of about 2 μm or less; 
 
 detecting a height of the mask layer by a height sensor of the laser drilling system, the mask layer providing a substrate surface; 
 determining one or more properties of the blind via, the one or more properties of the blind via comprising:
 a top diameter of the blind via and a bottom diameter of the blind via, the blind via having a height from the top diameter to the bottom diameter, the top diameter being greater than the bottom diameter; 
 a volume of the blind via, the volume corresponding to the top diameter, the bottom diameter, and the height of the blind via; or 
 a taper angle of about 80 degrees or more; 
 
 removing at least a portion of the mask layer by focusing a Gaussian laser beam emitted from the femtosecond laser source of the laser drilling system, under laser process parameters, at the substrate surface; 
 after removing the at least a portion of the mask layer, adjusting the laser process parameters based on signals from the height sensor regarding the height of the mask layer and the one or more determined properties; and 
 removing at least a portion of the dielectric layer within the volume by focusing the Gaussian laser beam using the beam expander, the collimator, and the galvanometer scanner, under the adjusted laser process parameters, to form the blind via. 
 
     
     
       17. A method of forming a blind via in a substrate, comprising:
 conveying the substrate to a scanning chamber of a laser drilling system having a galvanometer scanner, a beam expander, and a collimator coupled to a femtosecond laser source configured to emit a Gaussian laser beam, the substrate comprising:
 a conductive layer of about 2 μm or more in height, 
 a dielectric layer disposed on at least a portion of the conductive layer, and 
 a pre-etched mask layer disposed on at least a portion of the dielectric layer, the pre-etched mask layer comprises Al, Cu, W, Mo, Cr, or combinations thereof; 
 
 and the pre-etched mask layer has a height of 3 μm or less, the pre-etched mask layer having blind via openings to expose at least a portion of the dielectric layer, the at least a portion of the dielectric layer providing a substrate surface; 
 detecting the blind via openings of the pre-etched mask layer by a height sensor of the laser drilling system, the height sensor configured to determine a height of the pre-etched mask layer; 
 determining one or more properties of the blind via, the one or more properties of the blind via comprising:
 a top diameter of the blind via and a bottom diameter of the blind via, the blind via having a height from the top diameter to the bottom diameter, the top diameter being greater than the bottom diameter, and the top diameter corresponding to the blind via openings; 
 a volume of the blind via, the volume corresponding to the top diameter, the bottom diameter, and the height of the blind via; or 
 a taper angle of 80 degrees or more; 
 
 removing a first portion of the dielectric layer within the volume of the blind via, without causing more than half of the thickness of mask layer damage to the pre-etched mask layer, by focusing a Gaussian laser beam emitted from the femtosecond laser source of the laser drilling system, under laser process parameters, at the substrate surface; 
 after removing the first portion of the dielectric layer, adjusting the laser process parameters based on signals from the height sensor and the one or more properties; and 
 removing a second portion of the dielectric layer within the volume by focusing the Gaussian laser beam using the galvanometer scanner, the beam expander, and the collimator, under the adjusted laser process parameters, to form the blind via.